This invention relates to a case hardening, corrosion resistant, martensitic steel alloy and articles made therefrom and, more particularly, to such an alloy which, when case hardened and heat-treated, has an outstanding combination of case properties including high hardness with high temperature capability, corrosion resistance and metal-to-metal wear resistance: combined with outstanding core properties including ductility, impact toughness and fracture toughness.
Articles such as bearings and gears which possess a combination of excellent toughness, high temperature capability, and corrosion resistance as well as excellent case hardness and core ductility have been in demand to meet the more exacting operating conditions of aircraft engines and transmissions now under development. Presently known stainless steels, such as those described in U.S. Patent No. 2,590,835, issued to H. W. Kirkby and C. Sykes on April 1, 1952, and in U.S. Pat. No. 3,154,412 issued to A. Kasak et al. on Oct. 27, 1964, do not possess this requisite combination of properties and therefore are unsuitable for use in the fabrication of parts such as aircraft engine bearings.
Recent developments in the design of aircraft jet and turboprop engines and transmissions have placed more stringent demands on parts including bearings and gears; for instance, improvements in engine performance will require such parts to operate under increasingly severe loads and temperatures. Additionally, some new engine designs are more open to the environment than their predecessors, leading to increased risk of corrosion of parts such as bearings due to greater exposure to moisture and, for aircraft used in marine environments, chlorides during shutdown. Thus, a significant problem encountered by the aerospace industry is that engine and transmission bearings and gears fabricated from presently known alloys do not possess the combination of toughness, high temperature capability, and corrosion resistance as well as case hardness and core ductility required of such components by the aircraft designs currently under development.